What is AIDS?

Originally Published: March 1, 1994 - Last Updated / Reviewed On: November 26, 2007
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Dear Alice,

What is AIDS?

— Wondering

Dear Wondering,

AIDS is an illness that damages a person's ability to fight disease, leaving the body susceptible to ordinarily harmless infections and illnesses. AIDS stands for Acquired Immune Deficiency Syndrome. In the first years of the AIDS epidemic, there was some controversy about whether HIV causes AIDS, however researchers have since verified that being infected with HIV is the cause of AIDS. HIV stands for Human Immunodeficiency Virus. HIV infects certain types of white blood cells, mainly CD4 cells (also called helper cells or T4 cells), which are the cells in the immune system that normally protect us from disease. By damaging and killing the protective CD4 cells, HIV weakens the immune system.

A person with a damaged immune system is susceptible to various infections and illnesses, such as pneumonia, lymphoma (cancer of the immune system), and Kaposi's sarcoma (a malignant tumor of the connective tissue). These conditions are known as opportunistic infections, which are caused by microbes that take advantage of a weakened immune system, but are normally not harmful to healthy people. For people with AIDS, these conditions may often result in death.

HIV also infects and damages other types of cells, which can lead to additional problems. For example, damage to intestinal cells can lead to wasting (severe weight loss), and damage to nerve cells can cause neurological problems such as dementia and blindness.

Currently, there are two known types of HIV: HIV-1 and HIV-2. The differences pertain to their genetic structure. Primarily found in western Africa, HIV-2 is thought to be more difficult to transmit than HIV-1, and symptoms may take longer to appear. HIV-1 is more common and can be divided further into subtypes that vary geographically. However, both types of virus are transmitted in the same way and result in the same infections and illnesses.

The term "AIDS" refers to the most advanced stages of the course of HIV infection (and can also be called "advanced HIV disease"). The U.S. Centers for Disease Control and Prevention (CDC) develops the official definition for AIDS, which has changed over time. Since 1993, a clinical diagnosis of AIDS is given if someone has tested positive for HIV and meets at least one of the following criteria:

  1. has experienced one or more infections or illnesses associated with the severe immunodeficiency caused by HIV;
  2. has a CD4 cell count below 200 per cubic millimeter of blood.

For most HIV-infected people, the number of CD4 cells decreases gradually, although for some individuals, the drop may be sudden and dramatic. The decreasing CD4 count may result in symptoms and illnesses months or years before the actual progression to AIDS. (In healthy people, the CD4 count is usually between 500 and 1800.)

Without treatment, most people will develop AIDS within 10 to 15 years after being infected with HIV. However, this period can be much longer or shorter, depending on the individual. The good news regarding this devastating disease is that with effective treatment, people with HIV are living longer and healthier lives. The bad news is that it is estimated that over 33.2 million people are living with HIV or AIDS worldwide. In the United States, approximately 1.1 million people are living with HIV — and another 430,000 are living with AIDS. Globally, the majority of people living with HIV or AIDS are in the developing world, where access to treatment is limited or unavailable. Some encouraging news is that the number of new infections worldwide each year seems to be decreasing since the late 1990s; however with 2.5 million people receiving an HIV diagnosis yearly, the global community is still long way from extinguishing this destructive disease.

AIDS is often referred to in the media as a pandemic, meaning that it is an serious infection that is prevalent worldwide. Unfortunately many people who are infected with HIV have not been tested and are not aware of their infection. For example, public health officials estimate that in the United States 24-27 percent of people infected with HIV do not know they are infected. This creates a situation where HIV can spread more readily because people do not know they are able to transmit the infection to others and do not take precautions to prevent transmission.

To prevent HIV infection, people can:

  • Get tested — knowing your and sexual your partner(s)' HIV status is a step in knowing how to protect yourself
  • Practice safer sex — use condoms during anal, vaginal and oral sex
  • Avoid sharing needles — whatever their purpose, keep needles to yourself
  • Mothers infected with HIV can feed their infants baby formula instead of breast milk
  • Generally avoid contact with bodily fluids that carry HIV: blood, semen, vaginal fluids, and breast milk

Many pharmaceutical companies, universities, and research institutions are looking into drugs that help to treat HIV and AIDS related conditions, vaccines that may prevent infection, and of course a cure for the infection. However at this time no cure exists. Although there is no known cure for AIDS, effective treatment can slow the progression of HIV to AIDS, and help people with the infection live significantly longer, healthier lives.